1. Field of the Invention
This invention relates to emergency alarm systems, and more particularly to alarm systems having signal devices and voice announcement capabilities, which latter are arranged to automatically override the signal devices when desired.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
It is generally recognized that conventional fire alarm control panels have now been developed to the point where they are considered to be highly reliable. In buildings protected by such panels, when an alarm is sounded the occupants readily acknowledge the existence of a potential danger and quickly vacate the premises. However, many such conventional alarm systems give no indication of the severity of the danger, nor where the danger point is, or what would be the best course of action to pursue, as well as whether or not the alarm might be false. A situation having variables such as these could result in either inaction, or improper action and unnecessary injury.
The above drawback has been recognized, and improvements have been made by replacing the electromechanical bells and horns with loud speakers, and by providing an electronically-generated alarm signal, such as a siren, with a capability for voice override whereby a qualified person can communicate important information to the building occupants in an emergency situation.
There exist several methods of upgrading an existing alarm system to one having both alarm signal and voice capabilities. One approach is to completely scrap the existing alarm panel and replace it with a modernized one having the desired voice amplification and speaker circuitry. However, this is usually very costly. An alternative is to add an adapter module which can provide the desired combined voice and signal capabilities while still retaining the advantages of alarm detection and circuitry supervision of the already existing fire alarm control panel.
A prior arrangement involving the addition of a module to an existing fire alarm control panel, but with some important differences, is disclosed in U.S. Pat. No. 4,258,332 issued to Henry W. West on Mar. 24, 1981, and entitled LOUDSPEAKER AMPLIFIER, this patent having been assigned to Wheelock Signals, Inc.
One of the important differences found in the Wheelock system is that it internally supervises the output or speaker circuit, then transmits the data which identifies the trouble condition to the existing panel by means of a normally closed relay contact which interrupts the alarm-initiating circuit. A drawback of such an arrangement is that the trouble condition, which may not be in the nature of a failure, can prevent the control panel from seeing or sensing the actual alarm input.
Also, in the Wheelock module identified above, a fault must be detected by two separate circuits in order to initiate a trouble indication, one circuit being in the existing panel and the other being in the added Wheelock circuitry. The undesired result of this arrangement is that there are two chances for circuit failure. Also, the added circuitry is relatively complex, involving multiple components, thereby introducing an additional likelihood of component failure or system malfunction.
Another drawback of the Wheelock system is the modulation of direct current by both voice and alarm signals. This increases complexity and cost, and reduces reliability and flexibility in the units, since only amplifier/speakers designed especially for the Wheelock unit can be utilized.
Also, with prior devices where the speakers are remotely located so as to be out of the range of the party making an announcement, there is no positive indication of the operativeness of the voice circuitry. Under such circumstances if the person speaking cannot hear an echo from a speaker, he thus cannot be sure that the message is being properly transmitted.
Battery back-up is required on all fire alarm control panels, and where an added module is employed, the power drawn thereby must be provided by such batteries. In the Wheelock patented device, the "standby" current is found to be fairly high, even exceeding that of the fire alarm control panel itself. Accordingly either larger batteries are required by the Wheelock system, or else there results a sacrifice in the time available during which such a system can operate prior to shut-down caused by discharge of such batteries.